Sensor devices of this type are mainly used as rain sensors in motor vehicles for an automatic actuation of the windshield wipers and as light sensors for controlling the vehicle lighting. The use of traditional lenses to influence the beam path, such as, e.g., the lenses of the rain sensor shown in EP 1 068 112 B1, which are inclined towards the windshield, requires a comparatively large amount of space.
The use of holographic structures allows to realize smaller designs, as is known from, e.g., WO 03/026937 A1. These sensors are based on the principle of light diffraction with the aid of diffractive elements and therefore have the principle-induced drawback of a substantially lower useful luminous efficiency and a higher sensitivity to stray light.
DE 196 08 648 C1 proposes an optical sensor device in which the light entry and exit surfaces of the light conducting unit are configured in the form of Fresnel lenses. But since the surfaces of the light conductor in which the lenses are configured are perpendicular to the surface of the pane, this device requires a very large amount of space.
The basic disadvantages of prior art optical rain sensor or daylight sensor devices are found in the high production expense and in the unfavorable ratio of the sensor dimensions to the size of the use-sensitive surface area.
It is and object of the invention to provide an optical sensor device which, with optimum optical conditions, requires only very little structural space and has a sensitivity which is as low as possible to forefield objects and extraneous light.